1. Field of the Invention
The invention relates to a display device for a wristwatch having a luminescent surface for the background illumination of a display element.
2. Description of the Related Art
It is known from the prior art for digital displays for dates, days of the week and/or chronometer functions to be provided with numbers, in which case an analog movement mechanism simultaneously displays hours, minutes and seconds using hands.
Such timepieces have the advantage that they can be configured purely mechanically and thus do not require any energy source such as a battery and/or a solar cell in order to function. The problem with these analog timepieces, then, is to render the display visible in the dark. For this purpose, it is possible to provide a battery or rechargeable storage battery, by means of which a luminous unit is supplied with energy. U.S. Pat. No. 6,208,591 utilizes a luminescent layer which is arranged in and beneath the then transparent face. This luminescent layer illuminates the hands of the timepiece from behind. However, it is thus not possible to render additional digital information of the timepiece readable in the dark.
It was also known to apply luminescent materials to the hands in order for the latter to be luminous in the dark. The application of these materials to numbers which indicate the digital time units, however, is associated with two significant problems. On the one hand, the application of these materials results in these digital time displays becoming considerably thicker. Furthermore, such displays only appear in a window during the corresponding time unit and are otherwise covered by the face, with the result that they are not recharged to a sufficient extent.
There is no question of using radioactive products for sales of timepieces in the civilian sector.
Wristwatches, finally, are often provided exclusively with a digital display of time units. These watches are usually with an LCD display. Such watches require a power source.